At What Temperature Do Pipes Freeze?
Why 20°F Is the Number That Matters
Water inside a pipe doesn't freeze the instant outdoor air hits 32°F, because the pipe, the water moving through it, and the surrounding structure all hold some heat. The commonly cited threshold for real risk is sustained outdoor temperatures of 20°F or lower: at that point, pipes with little or no insulation exposed to that cold for several hours can freeze solid. Above 20°F, freezing is still possible, especially overnight or during a multi-day cold snap, but the timeline is generally longer.
What Actually Determines Whether Your Pipes Freeze
- Location: pipes running through unheated attics, crawlspaces, basements, garages, and exterior walls freeze first, since they don't benefit from the home's heating
- Insulation: an insulated pipe can tolerate meaningfully colder temperatures for longer than a bare one
- Wind exposure: wind chill on an exterior wall or exposed outdoor line accelerates heat loss beyond what the air temperature alone suggests
- Duration: a brief dip to 20°F overnight is less risky than several consecutive days below that mark
- Water movement: moving water resists freezing better than standing water, which is the entire logic behind the drip-faucet trick below
How to Prevent Frozen Pipes
- Let faucets drip on exposed or vulnerable lines when hard freezes are expected. Even a slow trickle keeps water moving and relieves pressure buildup if ice does form elsewhere in the line
- Know where your main water shutoff valve is before you need it, usually near where the main line enters the home or in the basement
- Insulate exposed pipes with foam pipe sleeves, or UL-listed heat tape/heat cable on pipes in the highest-risk unheated spaces (see our heat tape guide)
- Open kitchen and bathroom cabinet doors under sinks on exterior walls so warm household air can reach the plumbing (move cleaners and chemicals out of reach of kids first)
- Seal drafts near where pipes pass through exterior walls, foundations, and unheated spaces
- Keep the garage door closed if any water lines run through or near the garage
- Don't let the thermostat drop too low, even if you're away: most guidance recommends keeping the whole house, including rarely used rooms, no lower than 55°F during a hard freeze
- Disconnect and drain outdoor hoses and cover exterior spigots (see our faucet cover guide)
Free "Freeze Night" Checklist
WHEN THE FORECAST DROPS TO 20°F OR BELOW:
- ☐ Open cabinet doors under sinks on exterior walls
- ☐ Let faucets on exposed or exterior-wall lines drip slightly
- ☐ Disconnect garden hoses; cover outdoor spigots
- ☐ Close the garage door if water lines run through it
- ☐ Confirm the thermostat is set no lower than 55°F, everywhere in the home
- ☐ Locate your main water shutoff valve and confirm you can access it quickly
- ☐ If leaving home, ask a neighbor to check the house, or leave the heat on
Recommended Prevention Gear
These cover the three layers of protection that matter most: passive insulation you install once, an alert that tells you when conditions turn dangerous, and automatic protection if a pipe fails anyway.
Foam Pipe Insulation Sleeves
The cheapest and easiest first step for any exposed pipe in a basement, crawlspace, or garage: slip-on foam sleeves that slide over straight pipe runs in minutes, no tools required. They won't save a pipe from a sustained deep freeze on their own, but they raise the temperature threshold at which a pipe becomes vulnerable.
- No-tool slip-on installation
- Sold in multi-packs sized for standard 1/2" and 3/4" pipe
- Good first layer before adding heat tape on the highest-risk runs
Wireless Freeze & Temperature Alarm
A small battery or plug-in sensor placed near your most vulnerable pipe run (basement, crawlspace, unheated garage) that sends a phone alert if the ambient temperature drops toward freezing, so you can act before a pipe actually freezes rather than finding out after a trickle stops. It only alerts you; it doesn't do anything to the pipe itself, so you (or someone you can call) still need to be able to act on the alert.
- Phone alert well before pipe-freezing temperatures are reached
- Useful for vacation homes and rooms you don't check daily
- Pairs well with a wireless water leak detector for full coverage
Smart Water Shutoff Valve
A whole-home device installed at the main water line that can shut off water automatically when it detects a burst pipe or a sudden flow spike, limiting flood damage even if a freeze catches you away from home. Higher upfront cost than the other picks here, but the most serious protection against a burst-pipe worst case.
- Automatic shutoff on leak or flow-spike detection
- App alerts and manual remote shutoff
- Best paired with the leak sensors in our water leak detector guide
If a Pipe Has Already Frozen
If you turn on a faucet and get nothing or just a trickle during a cold snap, don't wait it out. See our step-by-step guide: Frozen Pipes: What to Do.
At What Temperature Do Pipes Freeze FAQ
At what exact temperature do pipes freeze?
Water itself freezes at 32°F, but household pipes are generally considered at real risk once outdoor temperatures reach 20°F or below. At that threshold, exposed or poorly insulated pipes can freeze in as little as six hours.
Does dripping a faucet actually prevent frozen pipes?
Yes. Moving water is more resistant to freezing than standing water, and a dripping faucet also relieves pressure that builds up between a faucet and a blockage if ice does form elsewhere in the line, which reduces the chance of a burst pipe.
Which pipes in a house are most likely to freeze?
Pipes running through unheated spaces: attics, crawlspaces, basements, garages, and exterior walls, especially on the side of the home facing prevailing winter wind. Outdoor spigots and hose bibs are also high-risk.
What temperature should I keep my thermostat at to prevent frozen pipes?
No lower than 55°F throughout the entire home, including rooms you don't use, during a hard freeze or while away. Closing vents or doors to "save energy" in a cold room can leave that room's pipes unprotected.
Can pipes freeze even if it's above 20°F?
Yes, especially for pipes with no insulation in a consistently cold, unheated space like a crawlspace or exterior-wall cavity, or during a multi-day cold snap. 20°F is a commonly cited risk threshold, not a hard line.